Whenever a compound crystal is cut normal to a randomly chosen direction, there is an overwhelming probability that the resulting surface corresponds to a polar termination and is highly unstable. Indeed, polar oxide surfaces are subject to complex stabilization processes that ultimately determine their physical and chemical properties. However, owing to recent advances in their preparation under controlled conditions and to improvements in the experimental techniques for their characterization, an impressive variety of structures have been investigated in the last few years. Recent progress in the fabrication of oxide nano-objects, which have been largely stimulated by a growing demand for new materials for applications ranging from micro-electronics to heterogeneous catalysis, also offer interesting examples of exotic polar structures. At odds with polar orientations of macroscopic samples, some smaller size polar nano-structures turn out to be perfectly stable. Others are subject to unusual processes of stabilization, which are absent or not effective in their extended counterparts. In this context, a thorough and comprehensive reflexion on the role that polarity plays at oxide surfaces, interfaces and in nano-objects seems timely.This review includes a first section which presents the theoretical concepts at the root of the polar electrostatic instability and its compensation and introduces a rigorous definition of polar terminations that encompasses previous theoretical treatments; a second section devoted to a summary of all experimental and theoretical results obtained since the first review paper by Noguera (2000 J. Phys.: Condens. Matter 12 R367); and finally a discussion section focusing on the relative strength of the stabilization mechanisms, with special emphasis on ternary compound surfaces and on polarity effects in ultra-thin films.

https://iopscience.iop.org/article/10.1088/0034-4885/71/1/016501/pdf

Polarity of oxide surfaces and nanostructures

-- Part C: 1. The continuum approach to crystal interfaces: basics. I: Theoretical framework. 2. Operators for orientation-dependent parameters. 3. Mechanics and thermodynamics of interfaces. 4. Equilibrium structures of junctions, edges and vertices. 5. Growth: kinematic wave theory revisited. 6. Kinetic behaviour of junctions, edges and vertices. 7. Structural phase transitions of a crystal surface as a branch of soliton physics. 8. Miscellaneous topics. II: Growth rate functions. 9. Analytic representations of R(n,A) functions. 10. Nonlinear networks and the 'assembled function' notation. 11. Physical aspects of assembling operations. 12. The systematic construction of R(n,A) functions by a sequence of assembling steps. 13. Notes on sphere-growth experiments. 14. Summary: Conclusions and outstanding questions. References. List of symbols, abbreviations and notations.

Morphology of crystals

Crystal morphologies are predicted from data stored in files in the CIF format (crystallographic information file standard of the International Union of Crystallography) on the basis of the Bravais–Friedel, Donnay–Harker model. Several simple improvements to the calculation are introduced with Win­XMorph, version 1.4.9, in conjunction with illustrations of the morphologies of quartz, sucrose, lactose, pyrite and lysozyme. The morphologies of the recently discovered pentamorphs of 1,8-dihydroxyanthraquinone are predicted. Win­XMorph is available free-of-charge for educational use.

/pdf/from-cif-to-virtual-morphology-using-the-winxmorph-program-uuo71klp3j.pdf

From CIF to virtual morphology using the WinXMorph program

Spinel-containing alumina-based refractory castables

Unidirectional seeded single crystal growth from solution of benzophenone

Structural morphology of YBa2Cu3O7-x

https://dspace.library.uu.nl/bitstream/handle/1874/17694/woensdregt_84_crystal.pdf?sequence=1

C.F. Woensdregt

Papers

Structural morphology of YBa2Cu3O7-x

Crystal morphology of ADP (NH4H2PO4): A qualitative approach

Crystal structural control on surface topology and crystal morphology of normal spinel (MgAl2O4)

Theoretical growth forms of natural garnets

Structural morphology of cotunnite, PbCl2, laurionite, Pb(OH)Cl, and SbSI